1. Field of the Invention
The present invention relates to a video recording apparatus for recording a static image in digital data, and more particularly to a video recording apparatus for compressing a fetched static image into data and recording the data in a random accessible digital data storage medium such as a hard disk or a magneto-optic disk and a monitoring apparatus using the video recording apparatus.
2. Description of the Related Art
A monitoring apparatus installed in a station, a bank or various stores usually records an analog video fetched from the monitor camera in a video tape. In recent years, however, a computer technology has been developed and a storage medium having a large capacity such as a hard disk, a CD-R, an MD or a DVD which can store a large volume of digital data can be provided inexpensively. Thus, a monitoring apparatus for recording a digital image fetched from image pick-up means such as the monitor camera in a digital data storage medium such as a hard disk has spread.
In the case in which a static image is to be fetched at a frame rate of one frame per second, for example, from a monitor camera installed in each of a plurality of monitoring places and is to be stored in a hard disk, even a hard disk having a large capacity is filled with monitoring data in a short time if the static image is stored as bit map data. Consequently, it is impossible to store, in the hard disk, monitoring data for a necessary monitoring time such as past 24 hours or the past week. For this reason, the static image is compressed into data and the data are stored, in the hard disk, as image data such as a JPEG (Joint Photographic Experts Group) or a GIF (Graphic Interchange Format).
In the case in which the static image fetched from the monitor camera is to be compressed into data, a data compression rate to be one of picture quality parameters in the same image is changed so that the capacity of one image data is varied and the number of image data which can be stored in a hard disk having a fixed capacity is also varied. Furthermore, the capacity of one image data greatly fluctuates with a variation in the contents of an image. For this reason, there is generated such a situation that image data for a predetermined monitoring time cannot be stored in the hard disk having a certain fixed capacity. Consequently, there is also supposed such a situation that monitoring data cannot be recorded during the generation of an accident because the hard disk is filled.
It is an object of the invention to provide a video recording apparatus capable of storing monitoring data for a predetermined monitoring time in a digital data storage medium and a monitoring apparatus using the video recording apparatus.
The object can be achieved by a video recording apparatus for storing image data sequentially fetched from image pick-up means in a digital data storage medium at a predetermined frame rate, comprising frame rate calculating means for calculating the frame rate depending on a picture recording time of the image data into the digital data storage medium.
The object can be achieved by a video recording apparatus for storing image data sequentially fetched from image pick-up means in a digital data storage medium at a predetermined frame rate, comprising frame rate calculating means for calculating the frame rate depending on a residual capacity of the digital data storage medium.
It is preferable that the frame rate calculating means should calculate a frame rate by setting image data for a past predetermined time of image data fetched from the image pick-up means to be a value which can be stored in the digital data storage medium. Furthermore, the frame rate calculating means calculates a frame rate based on a value of a picture quality parameter when image data are to be compressed and stored in the digital data storage medium. When the calculated frame rate is equal to or lower than a predetermined value, moreover, the frame rate is fixed to the predetermined value to regulate the value of the picture quality parameter. In addition, the frame rate calculating means reads a value of a prepared table to calculate a frame rate in place of the computation, and furthermore, sets image data having a high degree of importance to have a fixed frame rate and image data having a low degree of importance to have a lower frame rate when the frame rate is equal to or lower than a predetermined value.
It is more preferable that there should be provided data processing means for setting a data compression rate of image data having a high degree of importance to be lower than a data compression rate of image data having a low degree of importance, thereby storing the data in the digital data storage medium. Moreover, image data are set to have a high degree of importance when an alarm is generated or a trigger input is manually carried out. Furthermore, the data processing means deletes the image data having a low degree of importance or overwrites new image data having a high degree of importance to the image data having a low degree of importance when a residual capacity of the digital data storage medium is equal to or smaller than a predetermined capacity, and the degree of importance of image data is decided based on a value of a flag added to the image data.
It is more preferable that the data processing means should store only image data having a high degree of importance in the digital data storage medium when a residual capacity of the digital data storage medium is equal to or smaller than a predetermined capacity. At this time, moreover, a storage region for storing only image data having a high degree of importance is preset to be a dedicated region for each type of an alarm.
The object can be achieved by a monitoring apparatus comprising a monitor camera, an alarm generating device, the video recording apparatus having any of the structures described above which serves to input image data fetched from the monitor camera and an alarm fetched from the alarm generating device, and a monitor device for displaying, on a screen, the image data or image data obtained by reproducing image data stored in the digital data storage medium of the video recording apparatus.
Thus, in the case in which the image data sequentially input are to be stored in the digital data storage medium, a frame rate for storage is dynamically changed according to a picture recording time or the residual capacity of the storage medium so that image data for a predetermined time can be stored in the storage medium. Consequently, the picture recording time can be maintained. At this time, if a priority is given to image data having a high degree of importance and the image data are stored with a high picture quality, the limited storage medium capacity can be utilized effectively and an important image can be stored with a high density.